Check weight, method and system to ensure traceability of same

ABSTRACT

A check weight ( 1 ) that is used to check a gravimetric measuring instrument, specifically a balance, or to check a further weight, is provided with a means of identification. This marking which is applied on the outside surface of the check weight includes a permanently affixed machine-readable identification code ( 2 ) which makes the specific weight piece individually recognizable. This opens the possibility for a method whereby an individually identifiable check weight can be traced back in time. A system for tracing check weights back in time includes one or more reader devices ( 6 ) that serve to record the marking, one or more processors ( 10 ) wherein the machine-readable identification code can be converted back into an identification code that can be electronically processed, and one or more data storage units, in particular a database ( 8 ) serving to store at least the data contained in the identification code.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 35 USC §120 ofPCT/EP2008/058650, filed 4 Jul. 2008, which is in turn entitled tobenefit of a right of priority under 35 USC §119 from European patentapplication 07 11 1973.9, which was filed 6 Jul. 2007. The content ofeach of the applications is incorporated by reference as if fullyrecited herein.

TECHNICAL FIELD

The disclosed embodiments, which are in the field of metrology, relateto weights that are used to check balances and to check or measure otherweights.

BACKGROUND OF THE ART

Highly sensitive balances in particular, such as microbalances andultra-microbalances, analytical balances or precision balances, aresubject to influence factors which can lead to measurement deviationsover the course of time. Such balances therefore have to be checked on aregular basis in order to ensure that they produce accurate weighingresults. Such checks, so-called routine tests which are performed withina regulatory framework, are officially required in particular forbalances used in the fields of pharmacology, biotechnology and foodtechnology and are set down in FDA regulations (Food and DrugAdministration, U.S. Department of Health and Human Services). However,the manufacturers of balances also recommend to their customers thatbalances used in commercial applications be checked at regularintervals.

To determine deviations one uses check weights with defined nominalvalues. According to norm standards, for example the internationallyrecognized recommendation R111 published by OIML (OrganisationInternationale de Métrologie Légale), these kinds of check weights aresubject to tolerance limits within which the actual weight values haveto lie in relation to the nominal weight value. Under this tolerancesystem, the weights are divided into different weight classes accordingto different precision requirements. For example, the tolerance limitfor a one-milligram weight in class E1 (the highest accuracy class) is±0.003 mg, while the tolerance limit in class M1 (the lowest accuracyclass applicable to a one-milligram weight) is ±0.2 mg.

Check weights, as the term is used in the present context, should beunderstood to include weights of all kinds that are used to check and/orcalibrate and/or certify balances or weights particularly in areas thatare subject to regulatory control. These check weights are occasionallyalso called verification weights or calibration weights.

Check weights can be made of one solid piece or of several pieces ofmaterial. Single-piece check weights are made of one block of material,while check weights composed of more pieces have a cavity on the insidewhich is filled with so-called adjustment material up to the point wherethe nominal weight has been attained, whereupon the cavity is closedoff. It should be noted, however, that check weights made up of aplurality of pieces are not permitted in the highest accuracy classesaccording to OIML.

As the actual weight values of check weights will change over time dueto wear, this could have the consequence—in cases where these checkweights are used to check balances—that weighing results or industrialprocesses may also run outside their tolerance limits. One musttherefore make certain that in any given case the check weight toleranceis being met. To accomplish this purpose, the check weights themselvesare regularly checked against other check weights, so-calledverification standards. The time intervals for such verification checksare dependent on the respective accuracy class of the weights or on thearea of application and the particular circumstances of the application.

For each individual check weight, a certificate is issued on request,which states the actual weight value at the specific time, the nominalweight value, the accuracy class relative to a given class limit, aswell as a calibration I.D. number and the number of the calibrationcertificate. Each time another verification check, a so-calledrecalibration, is performed at a later date, a new certificate is issuedin which a new certificate number is assigned to the same weight, butthe same calibration I.D. number remains assigned to the weight.

The check weights or sets of check weights with different weight valuesare stored in special weight container cases for the distribution andlater, at their place of application, for storage by the user. In such acontainer case, there are appropriately dimensioned seating recessesprovided for each weight denomination, so that for example a 100-gramweight can be set with a precise fit only into the recess for 100-gramweights, but not into a recess for a 50-gram weight, while it would notcompletely fill out the recess for a 200-gram weight, so that acorrelation between weights and recesses is possible based on size. Thecertificates of the individual weight pieces are placed into thesecontainer cases so that in principle the connection between certificateand check weight is established. This is normally made evident by meansof a label that is affixed to the container case, on which thecalibration I.D. number is printed, and a further label on which thecertificate number is printed.

Due to the manual handling of the check weights in the process ofperforming the aforementioned routine tests, it is however easilypossible that the connection between the weight piece and its associatedcertificate and/or its calibration I.D. number gets lost. This canhappen for example if a balance is to be certified or calibrated for 400grams and if for this purpose—because there is no 400-gram weightavailable—a 200-gram weight piece and two 100-gram weight pieces areused instead. Regardless of whether the two 100-gram weight pieces arestored in the same container case or come from two different containercases, it is possible that handling errors will occur in the process,resulting in a mix-up of the two 100-gram pieces. The consequence ofthis is a wrong match between certificate and weight piece, which cannoteven be effectively checked, so that an error of this kind remainsundiscovered.

This method has the problem that there is no definite correlation thatties the certificate to the check weight, i.e. to the physical weightpiece itself. The handling of such check weights therefore requires theutmost diligence in order to ensure that the correct match betweencertificate and calibrated weight piece is permanently preserved. Still,there is no guarantee of achieving this goal. Inadvertent mix-ups cannotbe ruled out, nor can they be reliably detected after the fact.

In German laid-open application DE 40 06 375 A1, the concept ofequipping check weights with a code marking that represents the weightvalue is disclosed. This is realized by electronically storing theweight value in an electronic circuit which is contained in the weightpiece itself. This has the disadvantage that electrical contacts arenecessary for the transmission of the data from the weight piece to thebalance and vice versa and that because of these contacts, the weighthas to be set in a defined position and, in particular, special devicesare required which make the manufacture and use an error-prone process.Also, an electronic data storage is not totally error-resistant, so thatdata errors due to inappropriate handling of the check weights or alsodue to material fatigue, and thus calibration errors which occur as aresult, cannot be completely ruled out in this case either. Furthermore,check weights of this kind are expensive to produce.

Since the identification marking only contains the initial actual value,this coding system does not provide an individual identification of eachweight piece, but only a classification according to weight value. Underthe method described in this reference, an individual weight piece canbe traced back only insofar as the highest possible number of weightchecks that can be performed is entered in the electronic data storagedevice of the weight and each weight check is counted until this upperlimit is reached. Traceability beyond this time frame or in regard toother attributes such as place and date of manufacture, production lotnumber, etc., is impossible. A recall campaign which could be necessaryfor example in case of a manufacturing error in a production lot istherefore not possible for check weights that are identified in thisway.

It is therefore an objective to advance the design of a check weight insuch a way that the weight is permanently and individually traceable.

SUMMARY

This objective is met through the concept that the check weight itselfcarries an identification, specifically a marking by way of amachine-readable identification code on the outside of the weight,whereby each weight piece is made individually recognizable.

This concept has the advantage that the check weights can be permanentlyand reliably matched to their certificates and that all data can be readand processed by a machine and also be centrally stored if required.Mix-ups in the handling of the weights can thus to a large extent beeither avoided or reliably detected after they have occurred.Furthermore, for example if check weights that have been graded as OIMLClass E weights are found to be out of tolerance, such weights can bereassigned to a lower accuracy class without any problem.

Such a system of identification is advantageous for check weights ofmonolithic construction as well as those assembled from more than onepiece. Check weights are made of a metal or a metal alloy of aninvariant material density that is prescribed by the applicable normstandards.

Placing the identification code on the outside of the weight piece hasthe advantage that the processes of affixing the code and of reading itcan be realized in a simple manner.

In advantageous embodiments it is intended to implement theidentification code in a binary form of representation, in particular asa data matrix code or as a miniaturized barcode.

In preferred embodiments, the identification code includes a weightnumber that is uniquely assigned to the weight piece.

In practical further developed embodiments, the identification codecontains further data about the respective weight piece, including forexample the production lot number and specific dates, in particular theproduction date, the date when the marking was applied and/or the dateof the original calibration. This has the advantage that during weightchecking processes the data of the check weight can also be obtainedwithout accessing external databases or data backup on in-house storagemedia and such processes are therefore simplified and expedited.

A further objective is to provide a method through which check weightsof the foregoing description can be traced back in time. This isachieved by:

1) establishing an identification code,

2) converting the identification code into a machine-readable codeformat, and

3) placing the code in the machine-readable format as a marking or adistinguishing means on the weight piece.

The identification code contains essentially a weight number that isuniquely assigned to the check weight. However, it is also conceivableto set up the identification code in any other way that may be desired.The only essential requirement is that the identification code thusestablished has to be suitable for conversion into the intendedmachine-readable code that is to be put as a marking on the weightpiece. This process can be carried out immediately following theproduction of the check weights or also at a later point in time.Including the marking within the scope of the production process has theadvantage that every single weight piece is identifiable and thustraceable already at the completion of the production process. Applyingthe marking at a later time on the other hand has the advantage thatcheck weights that are already in use, in particular if the correlationwith their respective certificate has been lost, can afterwards be givenan identification which makes them traceable again.

It is intended to implement the code conversion in practice byconverting the identification code into a matrix code or a miniaturebarcode.

In an advantageous implementation of the marking method using a binaryform of representation, the marking process is performed with a laser.This has the advantage that the marking process can be performed withoutloss of material or at worst an only minimal loss and that the mark isat the same time connected in a permanent way to the weight piece. Knownlaser marking processes can produce an identification code pattern bymeans of a matte finish or through the method of the so-called annealingcolors.

Other inscribing methods that are well suited for the application of amarking include for example pin marking, etching, or electron beamscribing. But further methods, other than those mentioned here, arelikewise conceivable.

According to an advantageous further development of the method, afterthe marking has been applied to the check weight, the respectiveidentification code is permanently stored in a database. This createsthe advantageous possibility to systematically process and administratethe registered identification codes and the data of the weight piecesmarked with them. It is advantageous to also register and store thecertificate data in the database together with the identification code.Thus, the certificate data for individual single check weights canautomatically be kept available and sent out on request in a simple andreliable manner.

When a certificate is made out for a control weight, it contains aunique reference to the identification code. Particularly if theidentification code includes a weight number that is uniquely assignedto the weight, the weight number is also stated on the certificate.

As a checking-, calibrating- or recalibrating procedure can also includea comparison of a further check weight against a first check weight, inparticular against a verification standard, it is advantageous if theidentification code of the first check weight, specifically of theverification standard, is likewise recorded in the database, and it mayalso be stated on the certificate. In this way, a high degree oftraceability can be achieved.

The certificate data further include the calibration I.D. number, thecertificate number, the issue date of the certificate, the shape andmaterial of the check weight, the identity of the person performing theweight check, the conditions under which the weighing took place, theenvironmental conditions such as temperature and barometric pressure,the current weight value, as well as statistical data concerning theweight check.

As the weight pieces are recalibrated from time to time, it is apreferred practice to establish a history file for the specific weightbased on the chronological sequence of certificate data. With thehistory file, measured and/or stored data can be compared to those of apreceding certificate, the results can be processed further and, ifdesired, the results can be used to predict the extent to which theweights remain usable in the future.

When a routine test is performed, i.e. to check a balance by means of acheck weight, a program can be executed in the processor of the balancewhereby the identity of the check weight is investigated and validatedbefore the weighing test is started.

A further objective is to provide a system whereby check weights can betraced individually on a permanent basis. The described embodiments havethe advantage that all of the individually marked weight pieces can besystematically administrated and kept in particular under a centralizedcontrol, and that all of the data belonging to a given individual weightpiece can be accessed at any time. The one or more processors canconvert the marking code back into the underlying identification codeand directly make use of the latter. The at least one memory unit servesto save the identification code and, advantageously, also furtherregistered data (including for example the certificate data) belongingto the respective weight piece in a permanent and retrievable kind ofstorage. Such data are ideally kept available in a database whichprovides a centralized access and rapid systematic processingcapability. With this, the basis of the traceability of a given weightis established, which over the life of the check weight will for exampleallow a retroactive assessment of past wear and thereby also allowextrapolations for the future. This can for example include arecommendation to change the recalibration interval or also to assign aweight to a lower class if it has been found to exceed its applicabletolerance. Thus the highest possible quality in the surveillance ofcheck weights is assured, which increases the reliability of thebalances and/or weights that are verified with these check weights.

According to a further advantageous embodiment of the system, the atleast one processor is equipped with the capability to send out reportsbased on the results and/or extrapolations generated, such as forexample a notice regarding the expiration of a verification timeinterval. This has the advantage that the surveillance of the checkweights and the measurements performed with them can be systematicallyand reliably controlled from a central place, for example by themanufacturer of the weights. Thus there is assurance that the user ofthe check weights are alerted directly and reliably about any actionsthat need to be taken, which increases the quality of the respectivemeasurement systems.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the disclosed embodiments are explained in more detailwith references to the drawings, wherein:

FIG. 1 depicts an example of a check weight in side view;

FIG. 2 depicts a top view of the FIG. 1 check weight, wherein themachine-readable identification code in the form of a marking isindicated schematically;

FIG. 3 shows a magnified image of a matrix-type marking that is put on aweight;

FIG. 4 schematically depicts a system for the traceability of a checkweight; and

FIG. 5 is a flowchart diagram showing the time sequence of a routinetest.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a check weight 1. Of course, the proportionsof such check weights 1 can vary, or the weights 1 can have a completelydifferent shape depending in particular on the nominal weight value. Forexample the weights with the smallest nominal values are normallyconfigured as so-called wire weights or sheet metal weights.

FIG. 2 illustrates a check weight 1 of the same type as in FIG. 1, witha marking in the form of a matrix code 2 that contains an identificationcode. The shape and size of the matrix code 2 are not true to scale.Depending on the kind of marking being used, the shape and size of themarking can vary. However, in the case of the more accurate weightclasses E and F, the maximum size is prescribed by the norm standard.The way in which the marking is arranged on the weight piece canlikewise vary. Advantageously, the marking is placed on top in order tobe easily readable. However, it is just as conceivable to put themarking at some other location such as laterally or on the underside.

FIG. 3 shows an example for the design of such a marking 2 in the formof a matrix. As an example, the illustrated matrix 2 is atwelve-by-twelve array of matrix cells 3, 3′, wherein the two binaryvalues are represented in this case, respectively, by black matrix cells3 and white matrix cells 3′. The border rows of cells 4 and 4′ meetingat one corner of the matrix and the border rows 5 and 5′ meeting at theopposite corner each form a pattern which allows the reader device tofind the matrix code and to read and interpret it in the correctorientation. The border rows of cells with uniform binary values (black)running in the directions of the arrows 4, 4′ represent the so-calledfinder pattern, while the two border rows of cells with alternatingvalues running in the directions of the arrows 5, 5′ along therespectively opposite borders of the matrix represent the so-calledorientation pattern. The finder pattern 4, 4′ is used to find the matrixcode on the weight, while the orientation pattern 5, 5′ along therespectively opposite borders serves for the correct orientation in thereading and evaluating of the code. The cells enclosed by the two borderpatterns 4, 4′ and 5, 5′ represent the actual identification code.

The representation of the binary light and dark bits can be realized inthe manufacturing process for example by applying a matte finish to anoriginally polished surface for the matrix cells 3 shown in black in thedrawing. Other techniques of producing binary representations can alsobe used. One example are indentations produced for example through thepin-marking process, or a color change achieved by surface annealingwith a laser, or alternatively by etching.

FIG. 4 represents a schematic overview of a system to establish thetraceability of a check weight 1 as described herein. The reader device6 which is equipped with processor 10 reads the marking on the weight,in this case the matrix code 2. The processor 10 converts the matrixcode into an identification code and transmits the latter to a computer7 which is likewise equipped with one or more processors. The computer 7is connected to a database 8 which contains all of the data needed toissue a certificate 9. Based on the identification code, the computer 7is now enabled to retrieve the required data from the database 8 and toissue a certificate 9.

To ensure that every identification code is issued only once, theinscribing device (not shown here) which generates the marking, i.e. thematrix code 2, and which includes for example a laser, is equipped withappropriate software modules.

The database 8 has the capability to accept further data associated withthe stored identification code, in particular data that are required forthe certification, but also data that are generated only at later time,for example in connection with recalibrations of the check weight.

There can further be means which allow error checking of the matrix code2 that has been read into the system.

By way of the data connection 12 which is only symbolically indicated,data can be transmitted from the processor 11 of the computer 7 to otherprocessors and/or computers (not shown in the drawing) or received bythe latter. These processors can be in direct connection with theprocessor 11, or they can also be part of an intranet or be accessiblethrough the internet. Such computers can be installed for example at thecustomer's location or at other accredited metrological laboratories towhich the certificate data can be transmitted. Through the dataconnection 12, the identification code acquired by the reader device 6can be transmitted directly, i.e. without intermediate storage in thedatabase 8, to a processor at a remote location (not illustrated). Afurther data connection, for example to a balance on which calibrationchecks are performed (not shown), allows data from this checkingbalance, for example weighing result data, to be transmitted to theprocessor 11 of the computer 7, or data from the computer 7, for examplecertificate data, to be transmitted to the checking balance. Furthersystems configurations are also conceivable.

The flowchart diagram in FIG. 5 shows the time sequence of a routinetest for the checking of a balance with a weight piece 1 that is markedas described herein. The machine-readable identification code on theweight piece 1, for example in the form of a matrix code 2 as shown inFIG. 2, is used here for the purpose of verification and validation. Forexample, it is possible to ascertain whether the specific weight piece 1matches the weight piece described in the checking procedures, whichcould be internally generated or externally mandated procedures.

A program which is executed in the processor of the balance controls theprocess of the weighing check and instructs the user accordingly. As afirst step following the start, the weight piece 1 is presented to areader device 6 which reads the matrix code 2 and compares thecorresponding identification code to the data which are stored in thecomputer 7 for the weighing check. The computer 7 can be a computer setup separately from the balance, or it can be incorporated in the balancewhere it can be constituted essentially by the processor of the balance.If the identification code matches the code data of a permissible, i.e.registered, weight piece 1, the weight-checking process is allowed toproceed and the routine test can be continued. If no match is found forthe identification code, the weight-checking process is aborted and afailure message is issued. A record of the outcome can be produced by aprinter that is connected to the balance and/or to the computer 7. It isalso conceivable that a corresponding entry is made in the database 8that is connected to the computer 7.

The drawing figures represent a schematic illustration of embodimentsthat are meant only as examples. Different kinds of markings are alsoconceivable as well as different arrangements of the markings on theindividual weight pieces. It is also possible to include any otherdesired items of information in the code for the purpose of making thecentral traceability system more comprehensive.

1. A method for tracing an identifiable check weight back in time,comprising the steps of: establishing the identifiable check weightthrough the substeps of: providing a specific weight piece; forming anidentification code whereby the specific weight piece is given anindividual identity by which it can be recognized; converting theidentification code into a machine-readable code format; affixing theconverted code in the machine-readable format onto the specific weightpiece as a marking; storing the identification code in a database; andgenerating a calibration certificate that associates the specific weightpiece with the identification code; recalibrating the check weighthaving its identification code stored in the database; generating a newcertificate for the recalibrated check weight, based upon therecalibrating step; and establishing, in the database, a history filefor the recalibrated check weight, based on the chronological sequenceof certificate data therefor in the database.
 2. The method of claim 1,wherein: the converting step comprises converting the identificationcode into a matrix code or into a miniature barcode.
 3. The method ofclaim 1, wherein: the affixing step comprises applying themachine-readable code format to the weight piece by means of a laserbeam, pin marking, etching, or electron beam scribing.
 4. The method ofclaim 1, further comprising the steps of: calibrating a further checkweight against a first check weight having its identification codestored in the database; storing the identification code of the furthercheck weight in the database, associating it with the identificationcode of the first check weight; and generating a certificate thatassociates the further check weight with the identification code of thefirst check weight.
 5. The method of claim 1, further comprising thesteps of: establishing a set of certificate data for each of a pluralityof check weights; entering each certificate data set into the database;and correlating uniquely the identification code of each check weight tothe corresponding certificate data set in the database.
 6. The method ofclaim 5, wherein: the certificate data set comprises at least one of: acertificate number; a calibration identification number; an issue dateof the certificate; a description of the shape and material of the checkweight; an identity of a person performing the weight check; theconditions under which the weight check took place; the environmentalconditions such as temperature and barometric pressure; the currentweight value; and statistical data concerning the weight check.
 7. Themethod of claim 1, comprising the further steps of: comparing, in atleast one computer associated with the database, the data from therecalibrating step with data for at least one preceding certificate forthe check weight; and processing results from the comparing step furtherin the at least one computer.
 8. The method of claim 7, furthercomprising the step of: predicting, in the computer, the amount offurther use to be expected from the check weight, based on theprocessing results.
 9. The method of claim 1, further comprising thestep of: transmitting, from the computer, at least one of: certificatedata and a reminder notice regarding an approaching deadline for acalibration of the check weight.
 10. The method of claim 1, furthercomprising the step of performing a routine test to check a balance,comprising the substeps of: executing a program in a processor of thebalance that verifies and validates the identity of the check weight;and weighing the verified and validated check weight to check thebalance.
 11. A system for chronologically tracing an identifiable checkweight back in time, comprising: a check weight with an identificationcode that can be electronically processed, applied to the check weightin the form of a machine-readable marking; and a processor, connected toa database that associates the identification code of the check weightwith a first set of data associating the check weight with theidentification code at a calibration weighing and with at least onesecond set of data associating the check weight with the identificationcode at a recalibration weighing, the processor adapted for connectionto a balance on which the recalibration is performed.
 12. The system ofclaim 11, comprising: machine-readable programming, in the processor, toreceive and process further data associated with the check weight, inaddition to the identification code, the processed further data beingrecorded and stored in the database.
 13. The system of claim 12, furthercomprising: a communication device, operatively connected to theprocessor, for transmitting processed results of the machine-readableprogramming to other devices.
 14. The system of claim 11, furthercomprising: means, operatively connected to the processor, forgenerating a certificate associated with the check weight.
 15. Thesystem of claim 14, wherein: the database stores data associated withthe generated certificate, comprising at least one of: a certificatenumber; a calibration identification number; an issue date of thecertificate; the shape and material of the check weight; the identity ofthe person performing the weight check; the conditions under which theweighing took place; the ambient conditions such as temperature andbarometric pressure; the current weight value; and statisticalquantities concerning the weight check.
 16. A method for tracing anidentifiable check weight back in time, comprising the steps of:providing the identifiable check weight, comprising a specific weightpiece having a machine-readable code affixed thereto, themachine-readable code generated from an identification code thatprovides the specific weight piece an individual identity by which itcan be recognized; providing access to a database wherein are stored theidentification code and a calibration certificate that associates thespecific weight piece with the identification code; recalibrating thecheck weight having its identification code stored in the database;generating a new certificate for the recalibrated check weight, basedupon the recalibrating step; and establishing, in the database, ahistory file for the recalibrated check weight, based on thechronological sequence of certificate data therefor in the database.